Some patients with neutropenia have antibody in their serum which reacts with their own neutrophils as well as with the neutrophils of other individuals (alloantigens). The antigens involved are frequently not identifiable as known red cell, neutrophil or HLA antigens. We will study human neutrophil antigens to detect new antigenic specificities, determine their inheritance in families, and characterize the reaction of antibody and neutrophils. We will study microcapillary leukoagglutination, microgranulocytecytotoxicity, serum inhibition of glucose oxidation via the hexose monophosphate shunt during phagocytosis, and assays detecting surface immunoglobulin and complement components. Normal individuals and families from the MCV Twin Panel typed for known antigens will be used to define specificity.